This invention relates to cable manufacture, and more particularly to an installation for producing a fiber optic stranding element, of the type having at least one payout reel for a light-waveguide component, an extrusion head, a cooling device, and a device for receiving a finished stranding element. The invention also relates to a method of producing such a stranding element, of the type wherein a light-waveguide component passes through an extrusion head, a protective sheath is formed around the waveguide component in the extrusion head, and the sheath is then cooled. Finally, the invention further relates to the stranding element thus produced.
During the manufacture of fiber optic cable, the fiber component or components must be longer than the surrounding sheath or sheaths. One major problem which thus presents itself in such manufacture is that of controlling this excess length of the fiber waveguide component(s) as compared with the sheath component(s). The light-waveguide(s), formed of fibers exhibiting a certain fragility, must be loose in their protective sheath; and care must be taken that the deformation to which the stranding element will be subjected when it is wound on the takeup reels, then during handling and laying, is not apt to damage the fragile constituents of the fibers. European Pat. No. 0 015 425, for example, describes means which may be provided for ensuring that light-waveguide components are loose within their protective sheaths.
It is an object of this invention to provide an improved installation for producing fiber optic cable whereby the light-waveguide components are given the necessary excess length within the sheath or sheaths.
A further object of this invention is to provide an improved method of producing such fiber optic cable in order to achieve this excess length.
To this end, in the installation according to the present invention, of the type initially mentioned, the payout reel or reels are provided with brakes whereby the tension of the guide component or components can be regulated, the cooling device comprises a first vat adjusted for cooling the stranding element to a first temperature T.sub.1, a main withdrawal means for pulling the stranding element through the extrusion head and the first vat, a second vat adjusted for cooling the sheath to a second temperature T.sub.2 lower than the temperature T.sub.1, and auxiliary withdrawal means capable of pulling the stranding element through the second vat with as low a tractive force as possible, and the receiving device is capable of receiving and driving takeup reels for storing the stranding element at the exit of the auxiliary withdrawal means.
In the method according to the preseent invention, likewise of the type initially mentioned, the cooling is effected in two successive stages, the waveguide component and the sheath are subjected to predetermined tensile stresses during the first stage of cooling, whereas during the second stage, the waveguide component is slack and the sheath is subjected to as low a tensile stress as possible, and the cooling temperature obtained during the second stage is lower than that obtained during the first stage .